Magnon dispersion shift in the induced-ferromagnetic phase of the noncentrosymmetric MnSi

TL;DR

This study uses neutron scattering to observe how magnon dispersion in MnSi shifts asymmetrically due to Dzyaloshinskii-Moriya interaction, and how this shift can be reversed by changing the magnetic field direction.

Contribution

First experimental confirmation of asymmetric magnon dispersion shift in MnSi caused by Dzyaloshinskii-Moriya interaction in a field-induced ferromagnetic phase.

Findings

Magnon dispersion shifts asymmetrically along magnetic field direction.

Shift is reversible when magnetic field direction is reversed.

Dzyaloshinskii-Moriya interaction causes the dispersion shift.

Abstract

Small angle neutron inelastic scattering measurement has been performed to study the magnon dispersion relation in the field-induced-ferromagnetic phase of the noncentrosymmetric binary compound MnSi. For the magnons propagating parallel or anti-parallel to the external magnetic field, we experimentally confirmed that the dispersion relation is asymmetrically shifted along the magnetic field direction. This magnon dispersion shift is attributed to the relativistic Dzyaloshinskii-Moriya interaction, which is finite in noncentrosymmetric magnets, such as MnSi. The shift direction is found to be switchable by reversing the external magnetic field direction.